Methane pyrolysis in molten media: The interplay of physical properties and catalytic activity on carbon and hydrogen production

Methane pyrolysis is now considered a promising process for producing clean hydrogen and high-value carbon materials. However, it requires very high temperatures (above 1000 °C) due to the kinetic barriers posed by the stable C-H bond, and the production of carbon presents a significant challenge. While solid catalysts can lower the operational temperatures to some extent, they are hindered by carbon accumulation, which deactivates the catalysts and clogs reactors, thus limiting process scalability. Recently, molten media have emerged as potential catalysts for methane pyrolysis. These media offer numerous advantages, including high thermal conductivity and resistance to deactivation via sintering or coking. Despite these advantages, a comprehensive understanding of how the physical properties and intrinsic catalytic activities of molten media influence methane pyrolysis is lacking. This review addresses this gap by examining the roles of physical properties, mainly surface tension, and catalytic activity in methane conversion and carbon morphology. The analysis of apparent activation energies across various molten media indicates that their physical properties significantly impact methane reactivity, challenging the conventional notion of catalytic activity. In summary, this review explores the synergistic effects of molten media's physical and catalytic properties on methane pyrolysis, highlighting the potential for these systems to revolutionize the process by enhancing efficiency and reducing operational challenges. Understanding these interactions is key to advancing the scalability and applicability of methane pyrolysis technologies for sustainable hydrogen production. • Molten media’s physical and catalytic properties impact methane pyrolysis. • Physical properties influence methane reactivity beyond catalytic activity. • Surface tension affects bubble diameter, interphase phenomena, and thus conversion. • A linear relationship exists between surface tension and methane activation energy. • Surface tension aids graphene alignment and 2D carbon growth at bubble interfaces.